Wetting liquid composition for offset master plate

ABSTRACT

THE PRINTABILITY OF AN OFFSET MASTER PLATE CAN BE MARKEDLY IMPROVED BY USING A WETTING LIQUID COMPOSITION COMPRISING (A) AT LEAST ONE OF TRANSPARENT AND WATER INSOLUBLE FINE PARTICLES HAVING A PARTICLE SIZE OF NOT MORE THAN 0.1U SUCH AS COLLOIDAL SILICA AND ALUMINA, (B) AT LEAST ONE OF ALKALI METAL ALTS SUCH AS SULFATES, HALIDES AND NITRATES OF K AND NA, (C) AT LEAST ONE OF LOW MOLECULAR POLHYDRIC ALCOHOLS AND POLYALKYLENE OXIDES HAVING A MOLECULAR WEIGHT OF NOT MORE THAN 1000 SUCH AS POLYETHYLENE GLYCOL, PROPYLENE GLYCOL, DIETHYLENE GLYCOL AND HEXYLENE GLYCOL AND (D) AT LEAST ONE OF WEAK ORGANIC ACIDS SUCH AS CITRIC ACID, SUCCINIC ACID, TARTARIC ACID, ADIPIC ACID, ASCORBIC ACID AND PROPIONIC ACID. SAID COMPOSITION PREFERABLY HAS A PH VALUE OF ABOUT 4.0-5.6.

United States Patent 3,829,319 WETTING LIQUID COMPOSITION FOR OFFSETMASTER PLATE Shigeyoshi Suzuki and Norio Kobayashi, Kyoto, and

Kazuo Shimizu, Tokyo, Japan, assignors to Mitsubishi.

U.S. Cl. 106-2 4 Claims ABSTRACT OF THE DISCLOSURE The printability ofan offset master plate can be markedly improved by using a wettingliquid composition comprising (A) at least one of transparent and waterinsoluble fine particles having a particle size of not more than 0.1such as colloidal silica and alumina, (B) at least one of alkali metalsalts such as sulfates, halides and nitrates of K and Na, (C) at leastone of low molecular polyhydrie alcohols and polyalkylene oxides havinga molecular weight of not more than 1000 such as polyethylene glycol,propylene glycol, diethylene glycol and hexylene glycol and (D) at leastone of weak organic acids such as citric acid, succinic acid, tartaricacid, adipic acid, ascorbic acid and propionic acid. Said compositionpreferably has a pH value of about 4.0-5.6.

The present invention relates to a wetting liquid composition forimproving the printability of an offset master plate and moreparticularly to a wetting liquid composition effective for wetting apresensitized master plate, an offset master plate which utilizes silversalt diffusion transfer system (disclosed, e.g., in Japanese PatentPublication No. 14330/ 67 and Japanese Patent Application No. 72039/67corresponding to U.S.S.N. 71623) or a silver salt offset master platesuch as photolithographic plate containing the developer as disclosed inU.S. Pat. 3,146,- 104.

It is well known that the action of wetting liquid in offset printingoperation is to impart a uniform ink repellency to non-image areas(hydrophilic areas which do not accept ink) on a master plate, wherebysmooth operation can be attained and clear printed matter can beobtained.

However, as often experienced by printing operations, the conventionalwetting liquid is sometimes insufficient to obtain constant printedmatters even by suitable wetting operation.

Furthermore, the conventional wetting liquids in which various chemicalagents coexist have had difiiculties in stability in storage andmoreover have had difficulty in obtaining clear printed matters. Inaddition, stain of ground color is readily caused due to unnecessaryadhesion of ink to non-image areas of the printed matter. This isconsidered to occur due to kind of ink, condition of atmosphere(temperature or humidity of room), the number of wettings, etc.

On the other hand, printing operation for long period of time causesemulsification of wetting liquid by the action of oil components in ink.This emulsification prevents adhesion of ink to image areas to causebreaking of the image areas or stains of non-image areas with ink. Thewetting effect and the emulsification phenomenon have close relationwith each other and generally the Wetting liquids which have greatwetting effect tends to cause emulsification and those which cause noemulsification show substantially no wetting effect. Therefore, it is arequirement for obtaining wetting liquids having good durability tosuitably keep the balance between the two phenomena.

3,829,319 Patented Aug. 13, 1974 It has been recognized that theconventionally used wetting liquids which comprise one or more ofhydrophilic materials such as CMC, gum arabic, sodium alginate, glycolcompounds and metal salts of nitric acid, phosphoric acid, etc. are notsuitable in the long period printing. Moreover, the state of many ofthese wetting liquids are extremely changeable due to kind of plates,kind of inks and dispersion of printing conditions and are notpracticable. For example, when printing is conducted with use of anoffset master plate which utilizes silver salt diffusion transfer systemand which is obtained by undercoating a polyester film with hydrophilicsubbing layer and then coated thereon a surface layer which containsnuclei for physical development which are fine particles of heavy metalsor sulfides thereof and up to 30% by weight of said nuclei of a highmolecular weight compound (see U.S.S.N. 71632), the emulsification isespecially apt to occur and if the emulsification is controlled, thebalance with the wetting effect is lost to cause stain of the printedmatters.

In an attempt to eliminate the above defects, various stabilizers,dispersants and activators have been added, but such addition rathergives an effect on the aggregationprecipitation action and bufferingaction.

As the results of the inventors extensive researches on theabove-mentioned defects and undesirable phenomena in offset printing, ithas been found that a wetting liquid composition containing fourcomponents comprising (A) at least one of transparent and waterinsoluble fine particles having a particle size of not more than 0.1,u,especially sol of oxide or hydroxide of a metal belonging to GroupIII-IV of short form of the periodic table such as colloidal silica,alumina, etc., (B) at least one of organic or inorganic salts of alkalimetals, especially anhydrides such as sulfates, halides, nitrates of Kand Na. in some instance, those containing water of crystallization, (C)at least one of low molecular polyhydric alcohols and polyalkyleneoxides having a molecular weight of not more than 1000 such aspolyethylene glycol, propylene glycol, pentaerythritol, glycerol, etc.and (D) at least one of weak organic acids usually employed by oneskilled in the art for accelerating printability and maintaining pH atsuitable value, such as citric acid, succinic acid, tartaric acid,adipic acid, ascorbic acid, propionic acid, etc. has remarkably highstability and can extremely improve the printability of offset masterplates. The polyalkylene oxides having a molecular weight of not morethan 1000" means the commercially available polyalkylene oxides.

The above components (A) preferably have a particle size of no more than0.1;, more preferably 0.00l0.5g. The reason therefore is that when itbecomes aqueous dispersion, it must be transparent and must not losewater retention effect and that it must have compatibility with othercomponents. In this case, it seems that as the result of ionic bond andcovalent bond with alkali metal salt, these produce a stable dispersion.

It is most suitable to adjust the pH value after wetting to about4.0-5.6. This adjustment is effected with said weak acids or saltsthereof (e.g., sodium acetate, borax, sodium citrate).

Therefore, pH value outside said pH range causes conspicuous reductionof the printability and unstability of the liquid. Of course, saidliquid is in the form of aqueous dispersion.

In this case, the limitation of the amount of the components isnecessary and the fine particle component is preferably about 0.1-1%,especially about 0.5% as solid matter. The alkali metal salt componentis preferably 3-8 times, especially 4-6 times the amount of said fineparticles. The polyol compound is preferably about 5-10% ice althoughthe amount depends upon control of viscosity and stability. Thecomponent weak organic acid may be used in an amount necessary foradjustment of pH and preferably 0.1-l% by weight of the wettingcomposition.

Thus prepared liquid is diluted to about 10-20 times. The degree of thisdilution depends upon kind of plates, kind of ink and circumstance ofprinting (kind of printing machine, external weather conditions) andcannot be limited in a definite range. However, in the composition ofthe present invention, the degree of dilution of less than 10 timestends to cause emulsification phenomena while that of more than 20 timesresults in difliculty in wetting.

Furthermore, taking the discrimination and appearance of the liquid intoconsideration, coloring agents such as cobalt chloride, manganesechloride, phthalocyanine pigments, malachite green, ultramarine, etc.may be added in a slight amount.

Besides, if necessary, hydrophilic materials such as CMC, gum arabic,sodium alginate, vinyl-pyrrolidone, vinylimidazole, methyl vinyl ether,maleic anhydride, etc. which are wetting components experimentallyemployed by one skilled in the art, water miscible organic solvents suchas methanol, dimethylformamide, dioxane, etc. and ion-containingcompound disclosed in Japanese Patent Publication No. 10910/61 and US.Pat. 3.490,906 may also be added.

The present invention will be illustrated in the following Examples.

EXAMPLE 1 Part by weight Water 820 Succinic acid 6 Borax 8.4 Sodiumsulfate (anhydrous) 25 Cobalt chloride (hexahydrate) 2.5 Ethylene glycol100 Colloidal silica (20% liquid) 28 PH:4.8-

The liquid comprising the above components was diluted with water in anamount of 10 times that of the components to obtain a wetting liquid. Amaster plate was manufactured as follows: A polyester film base wasunder-coated in a thickness of 100p. and immersed in a sol prepared fromthe following formulation.

Palladium sulfide sol (I+IIIIII) PdCl g H01 ml 40 Water ml 1000 Na s g8.6 Polyethylene glycol ml 30 Alkyl ether ml 10 Water Y ml 1000 IIIMethylvinyl ether-maleic anhydride copolymer To thus obtained offsetmaster was transferred an image from a negative sheet by the silver saltdiffusion transfer process and then the offset master plate was wettedwith said wetting liquid and used for printing by the commerciallyavailable offset printing machine (printing conditions: roomtemperature=25 C. and relative humidity=70% 4 COMPARATIVE EXAMPLE 1 Theconventional wetting liquid comprising the following components wasdiluted with water to 10 times.

NH H PO 10 Ni(NO 6H O v 15 CMC 4 Glycerin Water to be made 1000 ml.

COMPARATIVE EXAMPLE 2 The wetting liquid of Example 1 from which sodiumsulfate and colloidal silica were omitted or replaced by sodium tertiaryphosphate was used.

Comparative example Stability=Degree of clearance of the liquid afterallowing to stand 7 days at constant; temperature and humidity.

Emulsitication state=Degree of clearance of the liquid and state ofwetting roller after about 1 hour from beginning of printing.

Stain of ground co1or=Degree of stain of 50th, 100th, 300th, 500th and1,000th printed matter.

(The wetting state was the same.)

The wetting effect according to the present invention was not greatlyaffected by difference in kind of ink and in conditions andsubstantially maintained the results of the above table.

EXAMPLE 2 Substantially the same effects as those of Example 1 wereobtained by substituting alumina sol for colloidal silica and a mixtureof 60 g. of polyethylene glycol and 20 g. of ethylene glycol forethylene glycol in Example 1.

EXAMPLE 3 G. 4-Phenyl catechol 5 Dibutyl phthalate 50 The abovecomponents were dispersed in 300 g. of 10% gelatin solution and theresultant dispersion was dispersed in a dispersion medium comprising 25cc. of 8% saponin solution and 180 cc. of water by colloid mill toobtain a developer dispersion. Furthermore, an aqueous dispersion havingthe following formulation was prepared.

G. The resultant developer dispersion Aqueous gelatin solution (10%) 400Aqueous saponin solution (15%) 50 Formalin liquid (2%) 5 Water 425 Theresultant aqueous dispersion was coated on a paper substrate to whichpolyethylene was laminated (coating amount: about 7 g./m. After fixationof said layer, a photosensitive liquid comprising the followingcomponents was further coated on said layer in an amount of 15 g./m.

AgCl emulsion (silver concentration 3.2 mol G. percent) 600 Aqueoussaponin solution (15% 40 Formalin liquid (2%) 7 Water 830 The followingfogged photosensitive liquid chemically fogged at higher than 40 C. forabout 40 minutes was further coated on said layer in an amount of about7 g./m.

G. AgCl emulsion (silver concentration 3.2 mol percent) 360 Water 200NaOH A N 24 Formalin liquid (2%) 5 H S0 (2N) 3.5 Aqueous saponinsolution (15%) Formalin liquid (2%) 2 Water 955 (Liquids I and II weremixed to obtain a coating liquid.)

Thus obtained olfset master plate was exposed through a line drawingoriginal and treated with an aqueous solution of Na CO (4%) for about 20sec. and furthermore with a 2% CH COOH stop solution for 1 minute. Then,this was passed through a 1% aqueous solution of phosphoric acid toobtain a master plate.

Olfset printing was conducted in the same manner as in Example 1 withuse of the same wetting liquid to obtain the similar results as those inExample 1.

What is claimed is:

1. A wetting liquid composition for an offset master plate, saidcomposition having a pH of about 4.0-5.6 and containing (A) transparentand water insoluble fine particles having a particle size of not morethan 0.1g selected from the group consisting of colloidal silica andalumina, (B) a member of the group consisting of potassiurn and sodiumsulfates, halides and nitrates, (C) a member of the group consisting oflow molecular weight polyhydric alcohols and polyalkylene oxides havinga molecular weight of not more than 1000, and (D) at least one weakorganic acid, the amount of component (A) being about 0.1-l%, that ofcomponent (B) being about 3-8 times that of component (A), that ofcomponent (C) being about 5-10% and that of component (D) being about0.110% by weight of the wetting liquid compo sition.

2. A wetting liquid composition according to claim 1 wherein (C) is amember of the group consisting of polyethylene glycol, propylene glycol,pentaerythritol, glycerol, diethylene glycol and hexylene glycol.

3. A wetting liquid composition according to claim 2, wherein (D) isselected from the group consisting of citric acid, succinic acid,tartaric acid, adipic acid, ascorbic acid and propionic acid.

4. A wetting liquid composition according to claim 1, wherein (B) issodium sulfate.

References Cited UNITED STATES PATENTS 3,028,804 4/1962 Neugebauer etal. 101-451 3,522,062 7/1970 Shimizu et a1 1062 3,547,632 12/1970 Nadeau101-451 3,696,746 10/1972 Harper 106-2 DAVID KLEIN, Primary Examiner US.Cl. X.R. 10l--451

